Seat belt latch sensor assembly

ABSTRACT

A mechanical engagement system such as a seat belt assembly includes a housing and a slider slidably received within the housing, the slider is configured for movement between a first position and a second position within the housing. A single magnet is associated with the slider for slidable movement therewith while a hall effect device is fixed relative to the housing. The hall effect device is fixed relative to the housing and aligned with at the single magnet when the slider is in the second position. The hall effect device is configured to generate an output signal indicative of a latch condition of the mechanical engagement system as applied to the sensor assembly.

TECHNICAL FIELD

[0001] The present invention relates generally latching systems such as a safety restraint system, and more particularly to a seat belt latch sensor assembly that can detect engagement of a seat belt and provide an electrical signal in response thereto.

BACKGROUND

[0002] Certain latching systems, or any other type of mechanical engagement system, typically require a way to determine when full engagement has been achieved between two mechanical parts. These mechanical parts may both be movable or one can remain stationary relative to the other. One example of such systems requiring accurate and dependable engagement sensing schemes are vehicle restraint systems.

[0003] Vehicles are provided with seat restraints systems such as seat belts in order to restrain occupants in the seat. The proper engagement and operation of the seat belt ensures the safety of a driver and his or her occupants.

[0004] Seat belts often incorporate sensors that provide data to other vehicle restraint vehicle systems such as airbags. Deployment of an airbag may partially depend on the information supplied by the sensor in the seat belt, such as a sensor may determine the presence of an occupant on the seat. In some applications, it may be desirable to suppress the deployment of an air bag. For example, if an airbag corresponding to an unoccupied seat deploys, an unnecessary repair expense occurs. In addition, such sensors can also be used to indicate that the seat belt is properly tightened and properly engaged or latched for proper reliance thereon. Determination of a latched, or unlatched, condition of the belt may also be used to determine how the airbag should be deployed. A latched condition will deploy the airbag softly, while still protecting against injury due to impact. An unlatched condition will deploy the airbag at a much harder and quicker pace since this is an indication of an occupant not wearing a safety belt.

[0005] Most of the sensors employed today as latch engagement detectors are of a mechanical switch type. These mechanical switches involve at least two pieces that are in and out of continuous frictional contact, thus producing wear and misalignment with aging. Wear and misalignment between the mechanical pieces will eventually result in a latch detection failure.

[0006] Accordingly, there is a need for a seat belt latch sensor assembly that minimizes or eliminates one or more of the problems set forth above.

SUMMARY OF INVENTION

[0007] It is an object of the present invention to minimize or eliminate one or more of the problems set forth in the Background on any mechanical engagement system. To describe the advantages of this invention, the seat belt latch assembly application will be described in detail and used throughout this document.

[0008] One advantage of the present invention is that it allows elimination of a mechanical contact switch subject to wear and failure to indicate positive latch engagement with a seat belt sensor assembly of the seat belt system. According to the invention, a seat belt sensor assembly comprises a housing, a slider slidably received within the housing, the slider being configured for movement between a first position and a second position within the housing, a single magnet associated with the slider for slidable movement therewith, a Hall effect device being fixed relative to the housing and protruding between the first and the second magnets when the slider is in the second position, the Hall effect device being configured to produce an output signal, the output signal being indicative of a latch condition of the seat belt as applied to said sensor assembly. A biasing member is preferably included for providing an urging force to the slider, the urging force urging the slider into the first position.

[0009] The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will now be described by way of example, with reference to the accompanying drawings, in which:

[0011]FIG. 1 is an assembly view of the seat belt sensor assembly used in accordance with the present invention;

[0012]FIG. 2 is a simplified, perspective view of the seat belt sensor bottom cover in accordance with the present invention;

[0013]FIG. 3 is an exploded view of the slider and one magnet in accordance with the present invention;

[0014]FIG. 4 is an exploded view of the seat belt sensor assembly in the unlatched position;

[0015]FIG. 5 is an exploded view of the seat belt sensor assembly in a first latched position with a first amount of tension applied, namely zero tension;

[0016]FIG. 6 is an exploded view of the seat belt sensor assembly in a second latched position with a second amount of tension applied;

[0017]FIG. 7 is an exploded view showing a Hall effect device and magnets in a position corresponding to the second latched position of FIG. 8;

[0018]FIG. 8 is an exploded view showing the magnets in a position corresponding to a third latched position and with a third amount of tension applied;

[0019]FIG. 9 is a perspective view of an alternative embodiment showing one magnet oriented in a different position with respect to the hall effect device mounted to a PCB of the seat belt sensor assembly in the unlatched position; and

[0020]FIG. 10 is a perspective view of the alternative embodiment of FIG. 9 illustrating the magnet oriented with respect to the hall effect devices in a latched position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Referring now to the drawings wherein like reference numerals are used to identify identical components, FIG. 1 is an assembly view of the seat belt tension sensor assembly generally indicated by 10. The seat belt tension sensor assembly 10 includes a bottom cover 12, a buckle 14, a slider 16, spring 18, a magnet 20, hook portions 22 and 22 a, biasing members 24 and 26, a spring 30, a release button 32 and an upper cover 34.

[0022] Bottom cover 12 and upper cover 34 form a housing 40, which may be constructed out of a lightweight, easily molded material such as plastic. Bottom cover 12 includes cavity 42 configured in size and shape to receive a printed circuit board (PCB) 44. PCB 44 may be mounted in cavity 42, for example, as shown. Printed circuit board 44 includes a switch or Hall effect device 50 or other sensor capable of detecting a magnetic field. Device 50 is arranged so that it can operably align with magnet 20 to detect when a seat belt is engaged, as described in greater detail below. As illustrated, bottom cover 12 also includes I-beam like structures 52, 54, and 56 that retain buckle 14 when slider 16, hook 22,22 a, spring 18 and biasing members 24 and 26 are assembled to buckle 14.

[0023] With reference to FIG. 2, a simplified, perspective view of the seat belt sensor bottom cover 12 is provided. Bottom cover 12 includes cavity 42 whereby PCB 44 is housed. PCB 44 is standard type that allows electrical components to be surface mounted. A surface mounted switch or sensor 50 is used to detect a positive latch condition. Latch 88 is shown in the unlatched position. It should be understood that with reference to the orientation of PCB 44 as shown, is exemplary only and not limiting in nature. Many other orientations with respect to the placement of PCB 44 in the bottom cover 12 are achievable and are known to those of ordinary skill in the art and are consistent with the teachings of the present invention, which relate principally to the inventive arrangement. Nonetheless, the following may be taken as a non-limiting illustrated embodiment.

[0024] Referring again to FIG. 1, buckle 14 is generally rectangular shaped adapted to fit inside housing 40 and includes a generally planar base 61. Buckle 14 provides the means for receiving the assembly of slider 16 and hook portions 22, 22 a. Buckle 14, as shown, also includes a pair of J-shaped extensions 60, 62. Buckle 14 also includes a centrally-disposed opening 63 defined in-part by a pair of opposing ledges 64 and 66. Opening 63 has a preselected lateral width, whose function will be described in greater detail below. Buckle 14 further includes a pair of side rails 68 ₁ and 68 ₂ extending generally normally from base 61, and having a preselected lateral width between inner surfaces thereof. Buckle 14 further includes elongated slots 69 ₁ and 69 ₂ which are formed into either side of side rails 68 ₁ and 68 ₂. The elongated slots 69 ₁ and 69 ₂ function to retain hook 22 a which provides support for release button 32. When release button 32, in latched condition, is pushed, button 32 pushes hook 22 a and allows hook 22 a to spin up releasing latch 88.

[0025]FIG. 1 shows slider 16 from the top. Slider 16 is provided to carry magnet 20 responsive to engagement with and partial and full insertion of a seat belt tongue (best shown in FIG. 2). Slider 16 includes a pair of tabs 70, and 72. Slider 16 further includes a cavity 74 which is configured to receive magnet 20. The lateral (side-to-side) width of cavity 74 is selected to be no greater than the predetermined width of opening 63. This allows cavity 74 to be placed “down” into opening 63 of buckle 14 during assembly. Tabs 70, 72 have a side-to-side lateral width that is no greater than the preselected width between the side rails 68 ₁, 68 ₂. Through the foregoing, tabs 70, 72 can slide on top of ledges 64, 66.

[0026]FIG. 3 is an exploded, bottom view of slider 16 and its accommodation of magnet 20. Distance—y—indicates a maximum possible width of cavity 74 in order to fit through cavity 63 of buckle 14. The forward and aft surfaces 73F and 73A respectively, of cavity 74 cooperates with the forward and aft edges of opening 63 to provide mechanical stop feature, thereby defining the longitudinal travel of slider 16. Magnet 20 is orientated having a south pole thereof directed toward device 50 (direction of magnetization on an axis defining a length thereof). In other words, magnet 20 is configured and disposed relative to device 50 such that a south pole of the maximum magnetic field created by magnet 20 is most proximate to device 50.

[0027] The design of cavity 74 provides that magnet 20 is orientated such that an optimum magnetic field intensity is created to be sensed by device 50. More specifically, magnet 20 is oriented with respect to top surface of surface mounted device 50 wherein the north side of magnet 20 is distal while the south side of magnet 20 is proximate device 50. Moreover, the arrangement allows better use of the travel distance of the slider (i.e., the useful range over which a latch condition sensing can occur).

[0028] It should be understood that with reference to the orientation of magnet 20 as shown, is exemplary only and not limiting in nature. Other orientations with respect to the placement of magnet 20 in slider 16 are achievable and are known to those of ordinary skill in the art and are consistent with the teachings of the present invention, which relate principally to the inventive arrangement. Nonetheless, the following may be taken as a non-limiting illustrated embodiment.

[0029] The location of magnet 20 when assembled with respect to slider 16 allows the Hall effect device 50 to align with magnet 20 when slider 16 moves away from a first position (FIG. 4) where little or no tension is applied (since the tongue is unlatched) into one of a plurality of second positions (FIGS. 5-8). A second position(s) may correspond to tension levels between zero (latched but no tension), to increasing levels of tension as the seat belt is cinched. During travel of slider 16, the Hall effect device 50 remains stationary in the bottom cover 12. The Hall effect device 50 will sense the strength of the magnetic field of the approaching magnet 20 as the magnet travels toward the Hall effect device 50 and corresponding to the strength of the magnetic field, the Hall effect device 50 will determine a binary latch condition of the seat belt (i.e., latched or unlatched), and will produce a signal that will determine whether or not to suppress any safety-related items 82 such as a hyper-tensioner, airbag, or pre-tensioner, etc. When a magnetic flux density as detected by the present invention does not exceed the pre-determined threshold, the system may be configured to suppress a passenger air bag. Alternatively, the controller may be configured to activate a corresponding passenger airbag when a sensed flux density is indicative of a non-positive latch condition.

[0030] In an exemplary embodiment, the Vcc of the Hall effect device 50 is 5 volts +/−0.5 volts DC. The voltage with no magnetic field present will be approximately 2.5v. As the magnet is brought into the proximity of the hall effect device, the voltage will increase to near Vcc or decrease to near ground, depending on the polarity of the magnet. Accordingly, as the voltage increases or decreases, so does the proximity of magnet 20 relative to device 50 indicative of a latch or unlatch condition of the seat belt. Of course, Vcc may have values greater than and less than 5 volts. In an exemplary embodiment, hall effect device 50 is a hall switch that is programmable to select a magnetic flux density in which the hall switch is turned “on” when the hall switch device 50 senses a flux density that exceeds the selected magnetic flux B_(ON). Likewise, hall switch device 50 is programmable to select a flux density B_(OFF), at which the hall switch 50 is switched “off”. It will be recognized by one skilled in the pertinent art that although it is preferred that the hall switch is programmable, other hall switches are contemplated using several types of Hall switches available which differ in their switching points and behavior to obtain desired switch “on” and “off” states.

[0031] With continued reference to FIG. 1, slots 60 and 62 allow hook 22 to hinge and thereby allow movement of the hook 22 when a latch (not shown) of the seat belt is inserted into assembly 10. Biasing members 24 and 26 provide biasing force and are held into place by a pair of tabs 41 and 43 of hook 22 and a pair of hooks 65 ₁ and 65 ₂ (not shown) located on either side of buckle 14. Biasing members 24 and 26 can be of either compression or tension type. Biasing members 24 and 26 provide the urging force that slider 16 must overcome in order to move from a first position to a second position (as described above).

[0032] In an exemplary embodiment, the biasing force of the members 24 and 26 is overcome when a force of about 5 to about 15 pounds is applied therefore causing slider 16 to move into the second position (FIGS. 5-8). Of course, and as such applications may require, the biasing force of members 24 and 26 to become overcome may vary. Accordingly, and when the urging force of members 24 and 26 are overcome, slider 16 travels towards the Hall effect device 50 and magnet 20 creates a magnetic field around the Hall effect device 50 causing a resulting signal to be sent through a plurality of wires 78 and sent to the control unit 80 indicative of positive latch engagement of the seat belt.

[0033]FIG. 1 also shows hook 22 a including wing like structures 23 ₁ and 23 ₂ which protrude out from elongated slots 69 ₁ and 69 ₂ (when assembled) and glide in a back and forth like manner when release button 32 is activated. Spring 30 is placed between hook 22 a on tab 25 and stub 86 of hook 22 which allows movement of the release button 32.

[0034] Once release button 32 is in place, upper cover 34 snaps over bottom cover 12 and the integral seat belt sensor assembly is complete. Accordingly, the seat belt sensor assembly 10 is easily assembled.

[0035] Referring now to FIG. 4, an exploded view of the seat belt sensor assembly 10 in an unlatched position is provided. When latch 88 is on the outside of sensor assembly, hook 22, hinged at buckle 14, is in the upright position as shown. The unlatched position allows slider 16 ₁, accommodating magnet 20, to be urged into the first position through spring 18. When the slider 16 ₁ is at the first position, magnet 20 is located away from hall switch 50 of PCB 44. Switch 50 is capable of reading the magnet field created by magnet 20 or more accurately, sensing an absence of a magnetic field from distal magnet 20 and registers a signal corresponding to the unlatched position. This signal may provide information to control unit 80 warning the driver to latch the seat belt via light 87 (FIG. 1), for example, when the vehicle is in use.

[0036]FIG. 5 represents an exploded view of the seat belt sensor assembly 10 in the latched position, with zero tension. When latch 88 is inside sensor assembly 10, hook 22 hinged at buckle 14 is in the closed position as shown in the upper part of FIG. 5. The latched position causes slider at a second position 16 ₂ specifically the magnet 20 thereof, to be substantially aligned with switch 50. Measurement X₁ is arbitrarily selected for purposes of illustration to place magnet 20 at a certain distance from central portion of Hall effect device 48. This distance registers a certain magnetic field strength whereby Hall effect device 48 produces an output signal accordingly. At this position, the magnetic field intensity sensed by sensor 50 is at a maximum with respect to travel between the first and second positions along axis 51.

[0037] When the slider is at the second position 16 ₂, a south pole end of magnet 20 is located above and proximate switch 50 of PCB 44. Switch 50 is capable of reading the magnet field created by magnet 20 to sense the presence of a magnetic field from magnet 20 and registers a signal corresponding to the position indicative of a positive latch condition. This signal may provide information to control unit 80 notifying the driver of positive latch engagement via light 87 (FIG. 1), for example, being turned off when the vehicle is in use. Switch 50 is preferably programmable to switch from “off” to “on” at a selected flux density value created by magnet 20 aligned therewith indicative of a latch condition. Switch 50 remains “on” as magnet 20 moves away from and out of alignment with switch 50 as tension is increased until the reducing flux density reaches a value indicative of an un-latch condition, at which point switch 50 changes state from “on” to “off”.

[0038]FIG. 6 shows tension is applied to the seat belt (not shown). Latch 88 moves in the direction of the arrow thereby creating a force necessary to move slider away from position 16 ₂ toward position 16 ₃.

[0039]FIG. 7 shows slider in position 16 ₃. Distance X₂ places magnet 20, residing in slider at position 16 ₃, at a certain distance from the Hall effect device 50. This distance X₂ correspond to a certain tension applied via latch 88. The relative position of sensor 50 and magnet 20 registers a certain magnetic field strength whereby Hall effect device 50 produces an output signal that corresponds to the intensity of the magnetic field created by the location of magnet 20. However, this field strength is above a threshold value for switching switch 50 from the “on” state to the “off” state indicating an unlatched condition.

[0040] If additional tension is applied, FIG. 8, distance X₃ places magnets 20 a and 20 b, residing in slider 16 ₄ at a distance defined by X₃ from the front edge of Hall effect device 48. However, again, the field strength associated with this distance is above a threshold value for switching switch 50 from the “on” state to the “off” state indicating an unlatched condition.

[0041] Many tension levels can be created when latch 88 is pulled and tightened, therefore measurements of X₂ and X₃ illustrate but a few of the plurality of possible tension measurements that may occur when operating the seat belt sensor tension assembly, while remaining in a latch condition.

[0042] Referring now to FIGS. 9 and 10, an alternative embodiment of a seat belt sensor assembly 100 having a contactless latch detector is illustrated. FIG. 9 illustrates an unlatched condition while FIG. 10 illustrates a positive latch condition indicative of positive engagement between latch 88 (not shown) and slider 116.

[0043]FIG. 9 illustrates the slider in a first position at 116 ₁ in an unlatched position. Slider 116 translates toward PCB 144 illustrated with arrow 130. In this manner, slider 116 is normal to a surface defining PCB 144 having device 150 extending therefrom. As latch 88 is brought into positive engagement with slider 116, magnet 120 is proximate device 150 and aligned therewith, as illustrated in FIG. 10. In this second position at 116 ₂, magnet 120 creates a magnetic flux density to turn “on” device 150 indicative of a positive latch condition. In this state, device 150 senses positive latch engagement and magnet 120 then moves in a direction indicated by arrow 132 when tension is applied.

[0044] When the slider is at the second position 116 ₂, magnet 120 is located proximate switch 150 of PCB 144 and magnet 120 is aligned therewith. Switch 150 is capable of reading the magnet field created by magnet 120 to sense the presence of a magnetic field from magnet 120 and registers a signal corresponding to the position indicative of a positive latch condition. This signal may provide information to control unit 80 notifying the driver of positive latch engagement via light 87 (FIG. 1), for example, being turned off when the vehicle is in use. Switch 150 is preferably programmable to switch from “off” to “on” at a selected flux density value created by magnet 120 aligned therewith indicative of a latch condition. Switch 150 remains “on” as magnet 120 moves away from and out of alignment with switch 150 as tension is increased until the reducing flux density reaches a value indicative of an unlatch condition, at which point switch 150 changes state from “on” to “off”.

[0045]FIG. 10 shows tension is applied to the seat belt (not shown). Latch 88 moves in the direction of arrow 132 thereby creating a force necessary to move slider away from position 116 ₁ toward position 116 ₂.

[0046] By eliminating a mechanical contact switch to indicate a positive latch condition that is subject to wear resulting in failure, and using a seat belt slider magnet in conjunction with a hall effect switch to detect latch engagement, a potential failure mode is eliminated and less parts are employed.

[0047] While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A seat belt sensor assembly comprising: a housing; a slider slidably received within said housing, said slider being configured for movement between a first position and a second position within said housing; a single magnet associated with said slider for slidable movement therewith; and a hall effect device being fixed relative to said housing and substantially aligned with said magnet when said slider is in said second position, said hall effect device being configured to generate an output signal, said output signal being indicative of a latch condition of the seat belt as applied to said sensor assembly.
 2. The seat belt sensor assembly of claim 1 further comprising: a biasing member for providing an urging force to said slider, said urging force urging said slider into said first position.
 3. The seat belt sensor assembly of claim 1 wherein said housing further comprises a hook to accept a latch of said seat belt.
 4. The seat belt sensor assembly of claim 2 wherein said hook further comprises a stop device.
 5. The seat belt sensor of claim 2 wherein said slider is adapted for receiving force from said latch.
 6. The seat belt sensor assembly of claim 1 wherein said Hall effect device produces a discrete signal.
 7. The seat belt sensor assembly of claim 1 wherein said Hall effect device is a hall switch.
 8. The seat belt sensor assembly of claim 7 wherein said Hall effect device is programmable.
 9. The seat belt sensor of claim 1 wherein said output voltage signal changes as a function of movement of said slider.
 10. The seat belt sensor of claim 1 wherein said output voltage signal changes as a function of a magnetic flux density created by the movement of said slider in relation to said hall effect device.
 11. The seat belt sensor of claim 10 wherein said output voltage signal switches from an “off” state to an “on” state at a first determined flux density value.
 12. The seat belt sensor of claim 11 wherein said output voltage signal switches from said “off” state to said “on” state when said slider is in said second position.
 13. The seat belt sensor of claim 11 wherein said “on” state is indicative of a positive latch condition of the seat belt.
 14. The seat belt sensor of claim 10 wherein said output voltage signal switches from said “on” state to said “off” state at a second determined flux density value.
 15. The seat belt sensor of claim 14 wherein said “off” state is indicative of an unlatch condition of the seat belt.
 16. The seat belt sensor assembly of claim 1 wherein said biasing member is a plurality of springs.
 17. A seat belt sensor assembly comprising: a housing; a slider slidably received within said housing, said slider being configured for movement between a first position and a second position within said housing; a single magnet associated with said slider for slidable movement therewith; and a hall effect device being fixed relative to said housing and aligned with said magnet when said slider is in said second position, said hall effect device being configured to generate an output signal, said second output signal being indicative of a latch condition of the seat belt as applied to said sensor assembly; wherein said hall effect device provides said output voltage signal to a control unit, said control unit communicates said latch condition of said seat belt to a safety restraint device.
 18. The seat belt sensor assembly of claim 17 wherein said safety restraint device is a light display.
 19. The seat belt sensor assembly of claim 17 wherein said safety restraint device is an airbag.
 20. The seat belt sensor assembly of claim 17 wherein said safety restraint device is a pre-tensioner.
 21. The seat belt sensor assembly of claim 17 wherein said output voltage signal changes as a function of a flux density created by the movement of said slider in relation to said hall effect device.
 22. The seat belt sensor assembly of claim 21 wherein said output voltage signal switches from an “off” state to an “on” state at a first determined flux density value.
 23. The seat belt sensor assembly of claim 22 wherein said output voltage signal switches from said “off” state to said “on” state when said slider is in said second position.
 24. The seat belt sensor assembly of claim 22 wherein said “on” state is indicative of a positive latch condition of the seat belt.
 25. The seat belt sensor assembly of claim 21 wherein said output voltage signal switches from said “on” state to said “off” state at a second determined flux density value.
 26. The seat belt sensor assembly of claim 23 wherein said “off” state is indicative of an unlatch condition of the seat belt.
 27. The seat belt sensor assembly of claim 21 wherein said hall effect device produces a discrete signal.
 28. The seat belt sensor assembly of claim 21 wherein said hall effect device is a hall switch.
 29. The seat belt sensor assembly of claim 28 wherein said hall effect device is programmable.
 30. A method to determine positive latch engagement of a mechanical engagement system, the method comprising: configuring a slider to be slidably received within a housing, said slider being configured for movement between a first position and a second position within said housing; associating a single magnet with said slider for slidable movement therewith; and fixedly disposing a hall effect device relative to said housing and aligned with said magnet when said slider is in said second position, said hall effect device being configured to generate an output signal, said output signal being indicative of a latch condition of the mechanical engagement system as applied to said sensor assembly.
 31. The method of claim 30, wherein said mechanical engagement system is a seat belt assembly. 